Friday, 27 February 2015

A new type of methane-based, oxygen-free life form that can metabolize and reproduce similar to life on Earth has been modeled by a team of Cornell University researchers. Taking a simultaneously imaginative and rigidly scientific view, chemical engineers and astronomers offer a template for life that could thrive in a harsh, cold world - specifically Titan, the giant moon of Saturn. A planetary body awash with seas not of water, but of liquid methane, Titan could harbor methane-based, oxygen-free cells.

Their theorized cell membrane, composed of small organic nitrogen compounds and capable of functioning in liquid methane temperatures of 292 degrees below zero, is published in Science Advances, Feb. 27. The work is led by chemical molecular dynamics expert Paulette Clancy and first author James Stevenson, a graduate student in chemical engineering. The paper's co-author is Jonathan Lunine, director for Cornell's Center for Radiophysics and Space Research.

Lunine is an expert on Saturn's moons and an interdisciplinary scientist on the Cassini-Huygens mission that discovered methane-ethane seas on Titan. Intrigued by the possibilities of methane-based life on Titan, and armed with a grant from the Templeton Foundation to study non-aqueous life, Lunine sought assistance about a year ago from Cornell faculty with expertise in chemical modeling. Clancy, who had never met Lunine, offered to help.

"We're not biologists, and we're not astronomers, but we had the right tools," Clancy said. "Perhaps it helped, because we didn't come in with any preconceptions about what should be in a membrane and what shouldn't. We just worked with the compounds that we knew were there and asked, 'If this was your palette, what can you make out of that?'"

On Earth, life is based on the phospholipid bilayer membrane, the strong, permeable, water-based vesicle that houses the organic matter of every cell. A vesicle made from such a membrane is called a liposome. Thus, many astronomers seek extraterrestrial life in what's called the circumstellar habitable zone, the narrow band around the sun in which liquid water can exist. But what if cells weren't based on water, but on methane, which has a much lower freezing point?

The engineers named their theorized cell membrane an "azotosome," "azote" being the French word for nitrogen. "Liposome" comes from the Greek "lipos" and "soma" to mean "lipid body;" by analogy, "azotosome" means "nitrogen body."

The azotosome is made from nitrogen, carbon and hydrogen molecules known to exist in the cryogenic seas of Titan, but shows the same stability and flexibility that Earth's analogous liposome does. This came as a surprise to chemists like Clancy and Stevenson, who had never thought about the mechanics of cell stability before; they usually study semiconductors, not cells.

The engineers employed a molecular dynamics method that screened for candidate compounds from methane for self-assembly into membrane-like structures. The most promising compound they found is an acrylonitrile azotosome, which showed good stability, a strong barrier to decomposition, and a flexibility similar to that of phospholipid membranes on Earth. Acrylonitrile - a colorless, poisonous, liquid organic compound used in the manufacture of acrylic fibers, resins and thermoplastics - is present in Titan's atmosphere.

Excited by the initial proof of concept, Clancy said the next step is to try and demonstrate how these cells would behave in the methane environment - what might be the analogue to reproduction and metabolism in oxygen-free, methane-based cells.

Lunine looks forward to the long-term prospect of testing these ideas on Titan itself, as he put it, by "someday sending a probe to float on the seas of this amazing moon and directly sampling the organics."

Stevenson said he was in part inspired by science fiction writer Isaac Asimov, who wrote about the concept of non-water-based life in a 1962 essay, "Not as We Know It." Said Stevenson: "Ours is the first concrete blueprint of life not as we know it."

The Curiosity robot confirms methane in Mars' atmosphere which may hint that life may have existed. An article published in Science confirms the existence of methane fluctuations in the atmosphere of Mars, as a result of the detailed analysis of data sent during 605 SOLs or Martian days. The tunable laser spectrometer in the SAM (Sample Analysis at Mars) instrument of the Curiosity robot has unequivocally detected an episodic increase in the concentration of methane in Mars' atmosphere after an exhaustive analysis of data obtained during 605 soles or Martian days.

This puts an end to the long controversy on the presence of methane in Mars, which started over a decade ago when this gas was first detected with telescopes from Earth. The controversy increased afterwards with the measurements obtained by orbiting satellites, some of which were occasionally contradictory. These new and incontrovertible data open paths for new research that can identify the sources that produce this gas--which could include some type of biological activity--and the mechanisms by means of which the gas is eliminated with such inexplicable speed.

Ever since the Telescope in the Mauna Kea Canada-France-Hawaii Observatory first announced the detection of methane in the Martian atmosphere, several other measurements of the gas have been conducted by means of a diversity of instruments, both remotely from earth, and also by means of satellites like the Mars Express and the Mars Global Surveyor.

Since methane can be the product of biological activity--practically all the existing methane in Earth's atmosphere originates in this way--this has created great expectations that Martian methane could also be of a similar origin.

These observations appeared to be contradictory. Some of them suggested a distribution pattern that was limited in space (with its source in the Northern hemisphere) and time (with a peak of concentration during summer in the Northern hemisphere and its subsequent vanishing in just a matter of months). Both facts are inexplicable by available photochemical and general circulation models, which are currently used to define our understanding of Martian atmosphere.

According to these models, if there really existed methane in Mars, it would remain there for an average 300 years, and during this period it would be homogeneously distributed across the atmosphere. Since we lack a model that can account for its generation, localization and swift disappearance, detections were all called in doubt, and the results were attributed to the instruments employed in their detection, which were working on the very limit of their capacity, and also to the fact that the concentration values of the gas that they yielded were of the ppbv order (parts per billion by volume).

"Within this context, and when we were all almost fully persuaded that the data we had so far collected were at the very least rough it not fully invalid, the expectations to decide on this were bestowed upon the capacity of the SAM instrument to come up with more precise measurements", says this researcher at the Andalusian Institute of Earth Sciences.

By means of its TLS unit, SAM has been detecting basal levels of methane concentration of around 0,7 ppbv, and has confirmed an event of episodic increase of up to ten times this value during a period of sixty soles (Martian days), i.e., of about 7 ppvb.

The new data are based on observations during almost one Martian year (almost two Earth years), included in the initial prediction for the duration of the mission (nominal mission), during which Curiosity has surveyed about 8 kms in the basin of the Gale crater.

During this period, which comprehends all the full cycle of Martian seasons, the reference to the environmental data collected by the meteorological REMS (Rover Environmental Monitoring Station) station has allowed for the establishment of possible correlations with the environmental parameters that this instrument records: relative humidity, temperature and atmospheric opacity. Data on atmospheric opacity was obtained both by the UV sensor in REMS and also by MastCam (Mast Camera), the camera at Curiosity, which is employed for support in atmospheric surveys.

REMS is an instrument that has been developed and it is being scientifically exploited by Spanish researchers, some of whom have been members of the team that has conducted this important research. The hypothetical existence of seasonal variations in methane concentration in correlation with certain environmental variables, in any case, will be only confirmed through sustained measurements in the future, specifically oriented to establish which factors can determine the sporadic emission and subsequent degradation of this gas in Mars. As far as the spatial disposition of the methane plumes, they have concluded that they are generated in very brief and weak events and in very specific places.

TLS is a two-channel tunable laser spectrometer which analyses in the infrared region--more specifically in a 2,7 μm wavelength through the first channel, and 3,27 μm through the second. The latter channel is specifically prepared for the detection of methane. It has a resolution of 0,0002 cm-1, which allows for the detection of methane through its spectrographic footprint of three very clearly defined lines, and the procedure which is applied (laser light absorption through a sample contained in a closed cell) "is simple, non-invasive and sensitive" as the article itself claims.

The containing cell can be full of Martian environment or as a vacuum to make contrasting measurements, which include some conducted through artificially increased concentrations, "which has resulted in a very reduced margin for error and guarantees the accuracy of results, which can now be deemed definitively conclusive", says Martín-Torres.

According to him, the new questions posed by these results far outnumber the answers it does provide. "It is a finding that puts paid to the question of the presence of methane in the Martian atmosphere, but it does pose some other more complex and far-reaching questions, such as the nature of its sources--which must lie, we believe, in one or two additional sources that were not originally contemplated in the models used so far. Among these sources, we must not rule out biological methanogenesis. Another new question is related to the bizarre evolution of methane in the Martian atmosphere after its emission. Both questions should be addressed in the future with specifically designed new research."

The newly arrived MAVEN (Mars Atmosphere and Volatile Evolution) from NASA will immediately provide continuity for the study of this subject, and in the near future the Trace Gas Orbiter (TGO), jointly developed by the European Space Agency (ESA) and the Russian Space Agency (Ruscosmos), which is also part of the ExoMars mission, will measure the concentration of methane at larger scale, and it will allow for the establishment of a framework to contextualize the results obtained, and deepen our knowledge of methane dynamics in Mars.

One of the biggest mysteries in galaxy evolution is the fate of the compact massive galaxies that roamed the early Universe. “When our Universe was young, there were lots of compact, elliptical-shaped galaxies containing trillions of stars,” says Alister Graham of Swinburne University of Technology. “Due to the time it takes for light to travel across the vastness of space, we see these distant galaxies as they were in our young Universe. However in the present-day Universe very few such spheroidal stellar systems have been observed.”

Closer to home, the central spheroid of our own Milky Way seems to have, in part, also existed when our Universe was young. We know that some of its stars are 12 billion years old, not much younger than the age of our Universe. The uncertain question is what fraction of our galaxy’s bulge may have subsequently been built via other processes.

The most popular theory had been that over time, galaxy mergers might have led to their destruction and transformation into larger elliptical galaxies. However there have not been enough galactic collisions to account for the reduction in the number of these compact spheroids.

The Swinburne astronomers, led by Professor Graham, have eliminated the need for this problematic theory because they have now located the missing galaxies. “They were hiding in plain sight,” Dr Bililign Dullo, co-author of the research, said. “The spheroids are cloaked by disks of stars that were likely built from the accumulation of hydrogen gas and smaller galaxies over the intervening eons.”

What’s more, the number of such hidden systems roughly matches the number of compact massive galaxies in the early Universe. “Unlike the massive dinosaurs that existed when the Earth was much younger, the galactic dinosaurs of our Universe are not extinct,” Professor Graham said. “They are simply embedded in large, relatively thin, disks of stars.”

Due to the enormity of modern galaxy surveys, it had become common practice to treat individual galaxies as single component entities. However by carefully disentangling each galaxy’s components, namely their inner spheroid and outer disk, the researchers uncovered the missing population.

“While the inner component is compact and massive, the full galaxy sizes are not compact,” Ms Giulia Savorgnan, a PhD student involved in the discovery, said. "This explains why they had been missed; we simply needed to better dissect the galaxies rather than consider them as single objects.”

Thursday, 26 February 2015

The MUSE instrument on ESO's Very Large Telescope has given astronomers the best ever three-dimensional view of the deep Universe. After staring at the Hubble Deep Field South region for only 27 hours, the new observations reveal the distances, motions and other properties of far more galaxies than ever before in this tiny piece of the sky. They also go beyond Hubble and reveal previously invisible objects.

By taking very long exposure pictures of regions of the sky, astronomers have created many deep fields that have revealed much about the early Universe. The most famous of these was the original Hubble Deep Field, taken by the NASA/ESA Hubble Space Telescope over several days in late 1995. This spectacular and iconic picture rapidly transformed our understanding of the content of the Universe when it was young. It was followed two years later by a similar view in the southern sky -- the Hubble Deep Field South.

But these images did not hold all the answers -- to find out more about the galaxies in the deep field images, astronomers had to carefully look at each one with other instruments, a difficult and time-consuming job. But now, for the first time, the new MUSE instrument can do both jobs at once -- and far more quickly.

One of the first observations using MUSE after it was commissioned on the VLT in 2014 was a long hard look at the Hubble Deep Field South (HDF-S). The results exceeded expectations.

"After just a few hours of observations at the telescope, we had a quick look at the data and found many galaxies -- it was very encouraging. And when we got back to Europe we started exploring the data in more detail. It was like fishing in deep water and each new catch generated a lot of excitement and discussion of the species we were finding," explained Roland Bacon (Centre de Recherche Astrophysique de Lyon, France, CNRS) principal investigator of the MUSE instrument and leader of the commissioning team.

The background image above shows the NASA/ESA Hubble Space Telescope image of the region known as the Hubble Deep Field South. New observations using the MUSE instrument on ESO's Very Large Telescope have detected remote galaxies that are not visible to Hubble. Two examples are highlighted in this composite view. These objects are completely invisible in the Hubble picture but show up strongly in the appropriate parts of the three-dimensional MUSE data.

For every part of the MUSE view of HDF-S there is not just a pixel in an image, but also a spectrum revealing the intensity of the light's different component colours at that point -- about 90 000 spectra in total. These can reveal the distance, composition and internal motions of hundreds of distant galaxies -- as well as catching a small number of very faint stars in the Milky Way.

Even though the total exposure time was much shorter than for the Hubble images, the HDF-S MUSE data revealed more than twenty very faint objects in this small patch of the sky that Hubble did not record at all. MUSE is particularly sensitive to objects that emit most of their energy at a few particular wavelengths as these show up as bright spots in the data. Galaxies in the early Universe typically have such spectra, as they contain hydrogen gas glowing under the ultraviolet radiation from hot young stars.

"The greatest excitement came when we found very distant galaxies that were not even visible in the deepest Hubble image. After so many years of hard work on the instrument, it was a powerful experience for me to see our dreams becoming reality," adds Roland Bacon.

By looking carefully at all the spectra in the MUSE observations of the HDF-S, the team measured the distances to 189 galaxies. They ranged from some that were relatively close, right out to some that were seen when the Universe was less than one billion years old. This is more than ten times the number of measurements of distance than had existed before for this area of sky.

For the closer galaxies, MUSE can do far more and look at the different properties of different parts of the same galaxy. This reveals how the galaxy is rotating and how other properties vary from place to place. This is a powerful way of understanding how galaxies evolve through cosmic time.

"Now that we have demonstrated MUSE's unique capabilities for exploring the deep Universe, we are going to look at other deep fields, such as the Hubble Ultra Deep field. We will be able to study thousands of galaxies and to discover new extremely faint and distant galaxies. These small infant galaxies, seen as they were more than 10 billion years in the past, gradually grew up to become galaxies like the Milky Way that we see today," concludes Roland Bacon.

Tuesday, 24 February 2015

In this image, an expanding shell of debris called SNR 0519-69.0 is left behind after a massive star exploded in the Large Magellanic Cloud, a satellite galaxy to the Milky Way. Multimillion degree gas is seen in X-rays from Chandra, in blue. The outer edge of the explosion (red) and stars in the field of view are seen in visible light from the Hubble Space Telescope.

Monday, 23 February 2015

Astronomers have identified the closest known flyby of a star to our solar system: A dim star that passed through the Oort Cloud 70,000 years ago. A group of astronomers from the US, Europe, Chile and South Africa have determined that 70,000 years ago a recently discovered dim star is likely to have passed through the solar system's distant cloud of comets, the Oort Cloud (image above). No other star is known to have ever approached our solar system this close - five times closer than the current closest star, Proxima Centauri.

In a paper published in Astrophysical Journal Letters, lead author Eric Mamajek from the University of Rochester and his collaborators analyzed the velocity and trajectory of a low-mass star system nicknamed "Scholz's star."

The star's trajectory suggests that 70,000 years ago it passed roughly 52,000 astronomical units away (or about 0.8 light years, which equals 8 trillion kilometers, or 5 trillion miles). This is astronomically close; our closest neighbor star Proxima Centauri is 4.2 light years distant. In fact, the astronomers explain in the paper that they are 98% certain that it went through what is known as the "outer Oort Cloud" - a region at the edge of the solar system filled with trillions of comets a mile or more across that are thought to give rise to long-term comets orbiting the Sun after their orbits are perturbed.

The star originally caught Mamajek's attention during a discussion with co-author Valentin D. Ivanov, from the European Southern Observatory. Scholz's star had an unusual mix of characteristics: despite being fairly close ("only" 20 light years away), it showed very slow tangential motion, that is, motion across the sky. The radial velocity measurements taken by Ivanov and collaborators, however, showed the star moving almost directly away from the solar system at considerable speed.

"Most stars this nearby show much larger tangential motion," says Mamajek, associate professor of physics and astronomy at the University of Rochester. "The small tangential motion and proximity initially indicated that the star was most likely either moving towards a future close encounter with the solar system, or it had 'recently' come close to the solar system and was moving away. Sure enough, the radial velocity measurements were consistent with it running away from the Sun's vicinity - and we realized it must have had a close flyby in the past."

To work out its trajectory the astronomers needed both pieces of data, the tangential velocity and the radial velocity. Ivanov and collaborators had characterized the recently discovered star through measuring its spectrum and radial velocity via Doppler shift. These measurements were carried out using spectrographs on large telescopes in both South Africa and Chile: the Southern African Large Telescope (SALT) and the Magellan telescope at Las Campanas Observatory, respectively.

Once the researchers pieced together all the information they figured out that Scholz's star was moving away from our solar system and traced it back in time to its position 70,000 years ago, when their models indicated it came closest to our Sun.

Until now, the top candidate for the closest known flyby of a star to the solar system was the so-called "rogue star" HIP 85605, which was predicted to come close to our solar system in 240,000 to 470,000 years from now. However, Mamajek and his collaborators have also demonstrated that the original distance to HIP 85605 was likely underestimated by a factor of ten. At its more likely distance - about 200 light years - HIP 85605's newly calculated trajectory would not bring it within the Oort Cloud.

Mamajek worked with former University of Rochester undergraduate Scott Barenfeld (now a graduate student at Caltech) to simulate 10,000 orbits for the star, taking into account the star's position, distance, and velocity, the Milky Way galaxy's gravitational field, and the statistical uncertainties in all of these measurements. Of those 10,000 simulations, 98% of the simulations showed the star passing through the outer Oort cloud, but fortunately only one of the simulations brought the star within the inner Oort cloud, which could trigger so-called "comet showers."

While the close flyby of Scholz's star likely had little impact on the Oort Cloud, Mamajek points out that "other dynamically important Oort Cloud perturbers may be lurking among nearby stars." The recently launched European Space Agency Gaia satellite is expected to map out the distances and measure the velocities of a billion stars. With the Gaia data, astronomers will be able to tell which other stars may have had a close encounter with us in the past or will in the distant future.

Currently, Scholz's star is a small, dim red dwarf in the constellation of Monoceros, about 20 light years away. However, at the closest point in its flyby of the solar system, Scholz's star would have been a 10th magnitude star - about 50 times fainter than can normally be seen with the naked eye at night. It is magnetically active, however, which can cause stars to "flare" and briefly become thousands of times brighter. So it is possible that Scholz's star may have been visible to the naked eye by our ancestors 70,000 years ago for minutes or hours at a time during rare flaring events. The star is part of a binary star system: a low-mass red dwarf star (with mass about 8% that of the Sun) and a "brown dwarf" companion (with mass about 6% that of the Sun). Brown dwarfs are considered "failed stars;" their masses are too low to fuse hydrogen in their cores like a "star," but they are still much more massive than gas giant planets like Jupiter.

The formal designation of the star is "WISE J072003.20-084651.2," however it has been nicknamed "Scholz's star" to honor its discoverer - astronomer Ralf-Dieter Scholz of the Leibniz-Institut für Astrophysik Potsdam (AIP) in Germany - who first reported the discovery of the dim nearby star in late 2013. The "WISE" part of the designation refers to NASA's Wide-field Infrared Survey Explorer (WISE) mission, which mapped the entire sky in infrared light in 2010 and 2011, and the "J-number" part of the designation refers to the star's celestial coordinates.

Saturday, 21 February 2015

During a manned mission to Mars, NASA Astronaut Mark Watney, played by Matt Damon, is presumed dead after a fierce sand storm and left stranded by his crew behind by his crew. But Watney, a biology genius and mechanical engineer, has survived and finds himself stranded and alone on the hostile planet when the Ares 3 mission is forced to evacuate their landing site in Acidalia Planitia due to a Mars-sized dust storm with high winds.

Watney is impaled by an antenna during the evacuation, destroying his EVA suit’s bio-monitor computer. His injury proves relatively minor, but with no way to contact Earth, Watney must rely on his scientific and technical skills to survive, growing potatoes in the crew’s Martian habitat and burning hydrogen to make water.

With only meager supplies, he must draw upon his ingenuity, wit and spirit to subsist and find a way to signal to Earth that he is alive. The movie is based on the must-read novel The Martian by Andy Weir published in 2012. This will be Scott's fourth sci-fi film since Alien, Blade Runner and Prometheus.

Thursday, 19 February 2015

"There seems to be a mysterious link between the amount of dark matter a galaxy holds and the size of its central black hole, even though the two operate on vastly different scales," says Akos Bogdan of the Harvard-Smithsonian Center for Astrophysics (CfA).

Bogdan and colleagues have found a distinct relationship between the mass of the dark matter halo and the black hole mass - a relationship stronger than that between a black hole and the galaxy's stars alone. This connection is likely to be related to how elliptical galaxies grow. An elliptical galaxy is formed when smaller galaxies merge, their stars and dark matter mingling and mixing together. Because the dark matter outweighs everything else, it molds the newly formed elliptical galaxy and guides the growth of the central black hole.

Every massive galaxy has a black hole at its center, and the heftier the galaxy, the bigger its black hole. But why are the two related? After all, the black hole is millions of times smaller and less massive than its home galaxy.

A new study of football-shaped collections of stars called elliptical galaxies provides new insights into the connection between a galaxy and its black hole. It finds that the invisible hand of dark matter somehow influences black hole growth.

This new research was designed to address a controversy in the field. Previous observations had found a relationship between the mass of the central black hole and the total mass of stars in elliptical galaxies. However, more recent studies have suggested a tight correlation between the masses of the black hole and the galaxy's dark matter halo. It wasn't clear which relationship dominated.

In our universe, dark matter outweighs normal matter - the everyday stuff we see all around us - by a factor of 6 to 1. We know dark matter exists only from its gravitational effects. It holds together galaxies and galaxy clusters. Every galaxy is surrounded by a halo of dark matter that weighs as much as a trillion suns and extends for hundreds of thousands of light-years.

To investigate the link between dark matter halos and supermassive black holes, Bogdan and his colleague Andy Goulding (Princeton University) studied more than 3,000 elliptical galaxies. They used star motions as a tracer to weigh the galaxies' central black holes. X-ray measurements of hot gas surrounding the galaxies helped weigh the dark matter halo, because the more dark matter a galaxy has, the more hot gas it can hold onto.

"In effect, the act of merging creates a gravitational blueprint that the galaxy, the stars and the black hole will follow in order to build themselves," explains Bogdan.

The paper describing this work has been accepted for publication in the Astrophysical Journal. This result relied on data from the Sloan Digital Sky Survey and the ROSAT X-ray satellite's all-sky survey.

The image at the top of the page shows the smallest known galaxy that contains an enormous black hole. New observations of the ultracompact dwarf galaxy M60-UCD1 have revealed a supermassive black hole at its heart, making this tiny galaxy the smallest ever found to host a supermassive black hole. Lying about 50 million light-years away, M60-UCD1 is a tiny galaxy with a diameter of 300 light-years, just 1/500th of the diameter of the Milky Way. Despite its size it is pretty crowded, containing some 140 million stars.

"We are fortunate enough to live on a planet that is ideal for the development of complex life," says New York University Biology Professor Michael Rampino. "But the history of the Earth is punctuated by large scale extinction events, some of which we struggle to explain. It may be that dark matter - the nature of which is still unclear but which makes up around a quarter of the universe - holds the answer. As well as being important on the largest scales, dark matter may have a direct influence on life on Earth."

Rampino's model of dark matter interactions with the Earth as it cycles through the Galaxy could have a broad impact on our understanding of the geological and biological development of Earth, as well as other planets within the Galaxy.

He concludes that Earth's infrequent but predictable path around and through our Galaxy's disc may have a direct and significant effect on geological and biological phenomena occurring on Earth. In a new paper in Monthly Notices of the Royal Astronomical Society, he concludes that movement through dark matter may perturb the orbits of comets and lead to additional heating in the Earth's core, both of which could be connected with mass extinction events.

The Galactic disc is the region of the Milky Way Galaxy where our solar system resides. It is crowded with stars and clouds of gas and dust, and also a concentration of elusive dark matter--small subatomic particles that can be detected only by their gravitational effects.

Previous studies have shown that Earth rotates around the disc-shaped Galaxy once every 250 million years. But the Earth's path around the Galaxy is wavy, with the Sun and planets weaving through the crowded disc approximately every 30 million years. Analyzing the pattern of the Earth's passes through the Galactic disc, Rampino notes that these disc passages seem to correlate with times of comet impacts and mass extinctions of life. The famous comet strike 66 million ago that led to the extinction of the dinosaurs is just one example.

What causes this correlation between Earth's passes through the Galactic disc, and the impacts and extinctions that seem to follow?

While traveling through the disc, the dark matter concentrated there disturbs the pathways of comets typically orbiting far from the Earth in the outer Solar System, Rampino observes. This means that comets that would normally travel at great distances from the Earth instead take unusual paths, causing some of them to collide with the planet.

But even more remarkably, with each dip through the disc, the dark matter can apparently accumulate within the Earth's core. Eventually, the dark matter particles annihilate each other, producing considerable heat. The heat created by the annihilation of dark matter in Earth's core could trigger events such as volcanic eruptions, mountain building, magnetic field reversals, and changes in sea level, which also show peaks every 30 million years. Rampino therefore suggests that astrophysical phenomena derived from the Earth's winding path through the Galactic disc, and the consequent accumulation of dark matter in the planet's interior, can result in dramatic changes in Earth's geological and biological activity.

In the future, he suggests, geologists might incorporate these astrophysical findings in order to better understand events that are now thought to result purely from causes inherent to the Earth. This model, Rampino adds, likewise provides new knowledge of the possible distribution and behaviour of dark matter within the Galaxy.

Wednesday, 18 February 2015

"We'll never find any direct evidence of land scum one cell thick, but this might be giving us indirect evidence that the land was inhabited," said Roger Buick, a University of Washington professor of Earth and space sciences. "Microbes could have crawled out of the ocean and lived in a slime layer on the rocks on land, even before 3.2 billion years ago."

A spark from a lightning bolt, interstellar dust, or a subsea volcano could have triggered the very first life on Earth. But what happened next? Life can exist without oxygen, but without plentiful nitrogen to build genes - essential to viruses, bacteria and all other organisms - life on the early Earth would have been scarce.

The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared roughly 2 billion years ago. Now research from the University of Washington looking at some of the planet's oldest rocks finds evidence that 3.2 billion years ago, life was already pulling nitrogen out of the air and converting it into a form that could support larger communities.

"People always had the idea that the really ancient biosphere was just tenuously clinging on to this inhospitable planet, and it wasn't until the emergence of nitrogen fixation that suddenly the biosphere become large and robust and diverse," said co-author Roger Buick, a UW professor of Earth and space sciences. "Our work shows that there was no nitrogen crisis on the early Earth, and therefore it could have supported a fairly large and diverse biosphere."

The authors analyzed 52 samples ranging in age from 2.75 to 3.2 billion years old, collected in South Africa and northwestern Australia. These are some of the oldest and best-preserved rocks on the planet. The rocks were formed from sediment deposited on continental margins, so are free of chemical irregularities that would occur near a subsea volcano. They also formed before the atmosphere gained oxygen, roughly 2.3 to 2.4 billion years ago, and so preserve chemical clues that have disappeared in modern rocks.

Even the oldest samples, 3.2 billion years old - three-quarters of the way back to the birth of the planet - showed chemical evidence that life was pulling nitrogen out of the air. The ratio of heavier to lighter nitrogen atoms fits the pattern of nitrogen-fixing enzymes contained in single-celled organisms, and does not match any chemical reactions that occur in the absence of life.

"Imagining that this really complicated process is so old, and has operated in the same way for 3.2 billion years, I think is fascinating," said lead author Eva Stüeken, who did the work as part of her UW doctoral research. "It suggests that these really complicated enzymes apparently formed really early, so maybe it's not so difficult for these enzymes to evolve."

Genetic analysis of nitrogen-fixing enzymes have placed their origin at between 1.5 and 2.2 billion years ago.

"This is hard evidence that pushes it back a further billion years," Buick said. Fixing nitrogen means breaking a tenacious triple bond that holds nitrogen atoms in pairs in the atmosphere and joining a single nitrogen to a molecule that is easier for living things to use. The chemical signature of the rocks suggests that nitrogen was being broken by an enzyme based on molybdenum, the most common of the three types of nitrogen-fixing enzymes that exist now. Molybdenum is now abundant because oxygen reacts with rocks to wash it into the ocean, but its source on the ancient Earth - before the atmosphere contained oxygen to weather rocks - is more mysterious.

The authors hypothesize that this may be further evidence that some early life may have existed in single-celled layers on land, exhaling small amounts of oxygen that reacted with the rock to release molybdenum to the water.

Future work will look at what else could have limited the growth of life on the early Earth. Stüeken has begun a UW postdoctoral position funded by NASA to look at trace metals such as zinc, copper and cobalt to see if one of them controlled the growth of ancient life.

A team of astronomers from National Astronomical Observatory of Japan observed Nova Delphini 2013 which occurred on August 14, 2013. Using the 8.2-meter Subaru Telescope High Dispersion Spectrograph (HDS) to observe this object, they discovered that the outburst is producing a large amount of lithium (Li). Lithium is a key element in the study of the chemical evolution of the universe because it likely was and is produced in several ways: through Big Bang nucleosynthesis, in collisions between energetic cosmic rays and the interstellar medium, inside stellar interiors, and as a result of novae and supernova explosions. This new observation provides the first direct evidence for the supply of Li from stellar objects to the galactic medium. The team hopes to deepen the understandings of galactic chemical evolution, given that nova explosions must be important suppliers of Li in the current universe.

The universe consisted primarily of hydrogen (H) and helium (He) immediately after the Big Bang except for very small amounts of Li. Since there are other elements heavier than H and He in the universe now, astronomers want to understand how the heavy elements -- such as carbon (C), oxygen (O), and iron (Fe) (which are present in our bodies) -- are produced. Such heavy elements are mainly produced in stellar interiors or supernovae. Then, they are supplied to the interstellar medium as seed materials for next generation of stars.

Li is the third lightest element following H and He, and is familiar to us as the base material for the Li-ion batteries used in PCs, smart phones, eco-cars, etc. Big Bang nucleosynthesis produced a very small amount of Li. Collisions between galactic cosmic rays (energetic atomic nuclei traveling with very high speeds) and atomic nuclei in the interstellar medium are also assumed to produce Li by breaking heavy elements' nuclei. Low-mass stars like the Sun, and events such as supernova explosions are also considered as candidates of Li production sites. Furthermore, scientists have been assuming that novae should also produce this element.

In the image above, a classical nova explosion is thought to occur on the surface of a white dwarf (center right) with a close companion star (center left; a sun-like main sequence or more evolved star). When the distance between two stars is close enough, the outer gas of the companion starts to accumulate on the surface of the white dwarf via an accretion disk. The thicker gas layer on the white dwarf increases its temperature and density. Then, nuclear reactions occur with a different way from those inside stars. In the case of stellar interiors, the huge energy produced by nuclear reactions in the core is balanced by the gravity of the surrounding gas, and then the reaction becomes stable. However, the nuclear reaction in a thin gas layer on the surface of a white dwarf has a different result. It becomes a runaway nuclear reaction, and results in an explosion that blows away the gas layer.

Because many sites and events can produce Li as described above, Li is the best indicator to probe the complete chemical evolution of the universe. Many scientists have studied this element by measuring the amount of Li found in various stars in our galaxy. This allowed them to estimate the amount produced through each process. Today, as a result of these indirect approaches, low-mass stars or nova explosions are thought to be the most important candidates for Li production in the current galaxy epoch. However, there have been no direct observations of the processes.

On August 14th, 2013, the well-known Japanese amateur astronomer Koichi Itagaki found a bright new star in the constellation Delphinus (Figure 3). This star, which was named Nova Delphini 2013 (=V339 Del), was at magnitude 6.8 at discovery and peaked at 4.3 mag within two days. It was the first naked-eye nova since 2007, when V1280 Sco was found. About 40 days later, in September 2013, a team of astronomers observed the nova to investigate the materials expelled by the explosion. That is when they found that the nova produced a large amount of Li.

Nova Delphini 2013 is considered one of the "classical novae". These brighten when explosive nuclear reactions occur in materials accumulated on the surface of a white dwarf star in a close binary system. The nuclear reactions are thought to produce a different series of elements (compared to those produced in stellar interiors or supernova explosions). Li is assumed to be an element typically produced in such outbursts. Historically, no one has been able to get good observational evidence for its production in nova explosions.

When the research group observed Nova Delphini 2013 using the Subaru Telescope, they used the High Dispersion Spectrograph to discern the constituents of the expelled materials from the nova explosion at four epochs (Figure 4).

Absorption lines originating from many elements such as H, He, and Fe are identified in the observed spectra (Note 4). Among them, there are sets of strong absorption lines in the ultraviolet (UV) range (wavelength ~313 nanometers) of the spectrum. Comparing these lines with other lines originating from H, calcium (Ca), and other elements, it turns out that they are originating from an isotope of beryllium (Be), 7Be, which is the fourth-lightest element in the universe.

In a classical nova, the isotopes of He (3He) and plentiful 4He transferring from the companion are fused together to form radioactive 7Be in a very high-temperature environment on the surface of a white dwarf. This radioactive isotope decays to form an isotope of lithium (7Li) within a short time (half-life of 53.22 days) (Figure 6). Because 7Li is very fragile in a high-temperature environment, it is necessary to transport 7Be to a cooler region in order to enrich Li in the interstellar medium. Novae completely fill this requirement. Therefore, they are assumed to be strong candidates as suppliers of Li in the universe.

This discovery of 7Be within 50 days after the nova explosion means that this explosion is actually producing a large amount of 7Li formed from 7Be. Because 7Be is found in the gas blobs blown away from the central region of the nova at high velocities (~1000 km/s), 7Li formed from this 7Be should not be destroyed in a high-temperature environment. This 7Li spreads into interstellar space, and will be included in the next generation of stars. It is found that the 7Be abundance in the gas blobs estimated from the strengths of their absorption lines is comparable to that of Ca. This amount of 7Be (= 7Li) should be quite large, given that Li is known as a very rare element in the universe.

The amount of Li rapidly increases in the galaxy in the current epoch, where the amounts of heavy elements have increased. Therefore, it has long been speculated that low-mass stars with longer lifetimes should be among the major suppliers of Li in the universe. Because nova explosions occur in binary systems evolved from such low-mass stars (especially 3He-rich companion, which is necessary to produce 7Be), they are strong candidates as Li suppliers. The observations made using the Subaru HDS provide the first strong evidence to prove that novae produce significant amounts of Li in the universe. This discovery confirms the chemical evolution model from the Big Bang to the present universe, as predicted by scientists.

This research was published in Nature on February 19, 2015, titled "Explosive lithium production in the classical nova V339 Del (Nova Delphini 2013)".

Tuesday, 17 February 2015

New research shows that a burst of evolutionary innovation in the genes responsible for electrical communication among nerve cells in our brains occurred over 600 million years ago in a common ancestor of humans and the sea anemone. Many of these genes, which when mutated in humans can lead to neurological disease, first evolved in the common ancestor of people and a group of animals called cnidarians, which includes jellyfish, coral, and sea anemones.

"Our research group has been discovering evidence for a long time that most major signaling systems in our neurons are ancient, but we never really knew when they first appeared," said Timothy Jegla, an assistant professor of biology at Penn State University, who led the research. "We had always assumed that we would be able to trace most of these signaling systems to the earliest nervous systems, but in this paper we show that this is not the case. It looks like the majority of these signaling systems first appear in the common ancestor that humans share with jellyfish and sea anemones."

Electrical impulses in nerve cells are generated by charged molecules known as ions moving into and out of the cell through highly specialized ion-channel proteins that form openings in the cell membrane. The new research focuses on the functional evolution of the genes that encode the proteins for potassium channels -- ion channels that allow potassium to flow out of nerve cells, stopping the cell's electrical impulses. "The channels are critical for determining how a nerve cell fires electrical signals," said Jegla. "It appears that animals such as sea anemones and jellyfish are using the same channels that shape electrical signals in our brains in essentially the same way."

"Humans and sea anemones went their separate ways evolutionarily speaking roughly 600 million years ago," said Jegla, "so we know that the mechanisms we use to generate impulses in our neurons must be at least that old." The team then tried to trace these channels back even further in evolutionary time -- to the very origins of the nervous system. "One of the exciting recent findings in evolutionary biology is that the nervous system might be much older than the ancestor of sea anemones and humans," Jegla said. Recent genome sequences from comb jellies, which also have nervous systems, show that they are a more ancient group of animals than sea anemones and might even be the oldest type of animals that are still living today. "When we looked at comb jellies, we found that the potassium channels looked very different -- most of the channel types found in humans were missing," said Jegla. "We could trace only one kind of the human potassium channels that we looked at all the way back to comb jellies, but we find almost all of them in sea anemones."

The implication is that many of the mechanisms we use to control electrical impulses in our neurons were not present in the earliest nervous systems. The team did find many different potassium channels in comb jellies, but they appear to have evolved independently after the comb jelly lineage split from that of our ancestors. "We don't know how complex electrical signaling is in living comb jellies, but it probably wasn't very complex in our common ancestor," said Jegla. The team now is interested in figuring out what drove the burst of innovation in ion channels in our common ancestor with sea anemones.

"We don't yet understand why our ion channels evolved at that time, but the changes in the ability of nerve cells to generate electrical signals must have been revolutionary," said Jegla. "Our current favorite hypothesis is that neurons capable of directional signaling might have evolved at this time." In human nervous systems, most nerve cells have a polar structure with separate regions for inputs and outputs. This allows for directional information flow and highly complex circuits of nerve cells, but it requires a huge diversity of ion channels to shape the electrical signals as they pass through the polar nerve cells. "If our hypothesis turns out to be correct, we may be able to gain some important insights into how nerve cells and circuits evolved by studying sea anemones," said Jegla. "There is a lot that remains to be discovered about how we build polar neurons, and we can use evolution to point out the really important mechanisms that have been conserved through animal history."

Monday, 16 February 2015

It was on Feb. 14, 1990, that the Voyager 1 spacecraft looked back at our solar system and snapped the first-ever pictures of the planets from its perch at that time beyond Neptune, capturing Neptune, Uranus, Saturn, Jupiter, Earth and Venus from Voyager 1's unique vantage point. A few key members did not make it in: Mars had little sunlight, Mercury was too close to the sun, and dwarf planet Pluto turned out too dim. The image of Earth contains scattered light that resembles a beam of sunlight, which is an artifact of the camera itself that makes the tiny Earth appear even more dramatic. Voyager 1 was 40 astronomical units from the sun at this moment. One astronomical unit is 93 million miles, or 150 million kilometers.

Taking these images was not part of the original plan, but the late Carl Sagan, a member of the Voyager imaging team at the time, had the idea of pointing the spacecraft back toward its home for a last look. The title of his 1994 book, "Pale Blue Dot," refers to the image of Earth in this series.

"That's here. That's home. That's us." wrote Sagan in "Pale Blue Dot". "On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. ... There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world."

"Twenty-five years ago, Voyager 1 looked back toward Earth and saw a 'pale blue dot,' " an image that continues to inspire wonderment about the spot we call home," said Ed Stone, project scientist for the Voyager mission, based at the California Institute of Technology, Pasadena.

"After taking these images in 1990, we began our interstellar mission. We had no idea how long the spacecraft would last," Stone said.

Today, Voyager 1, at a distance of 130 astronomical units, is the farthest human-made object from Earth, and it still regularly communicates with our planet. In August 2012, the spacecraft entered interstellar space - the space between the stars -- and has been delivering data about this uncharted territory ever since. Its twin, Voyager 2, also launched in 1977, is also journeying toward interstellar space.

"All stars form in dense clouds of dust and gas," said Adam Leroy, an astronomer formerly with the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, and now with The Ohio State University in Columbus. "Until now, however, scientists struggled to see exactly what was going on inside starburst galaxies that distinguished them from other star-forming regions."

Starburst galaxies transmute gas into new stars at a dizzying pace - up to 1,000 times faster than typical spiral galaxies like the Milky Way. To help understand why some galaxies "burst" while others do not, an international team of astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to dissect a cluster of star-forming clouds at the heart of NGC 253, one of the nearest starburst galaxies to the Milky Way.

ALMA changes that by offering the power to resolve individual star-forming structures, even in distant systems. As an early demonstration of this capability, Leroy and his colleagues mapped the distributions and motions of multiple molecules in clouds at the core of NGC 253, also known as the Sculptor Galaxy.

Sculptor, a disk-shape galaxy currently undergoing intense starburst, is located approximately 11.5 million light-years from Earth, which is remarkably nearby for such an energetic star factory. This proximity makes Sculptor an excellent target for detailed study.

"There is a class of galaxies and parts of galaxies, we call them starbursts, where we know that gas is just plain better at forming stars," noted Leroy. "To understand why, we took one of the nearest such regions and pulled it apart - layer by layer - to see what makes the gas in these places so much more efficient at star formation."

ALMA's exceptional resolution and sensitivity allowed the researchers to first identify ten distinct stellar nurseries inside the heart of Sculptor, something that was remarkably hard to accomplish with earlier telescopes, which blurred the different regions together.

The team then mapped the distribution of about 40 millimeter-wavelength "signatures" from different molecules inside the center of the galaxy. This was critically important since different molecules correspond to different conditions in and around star-forming clouds. For example, carbon monoxide (CO) corresponds to massive envelopes of less dense gas that surround stellar nurseries. Other molecules, like hydrogen cyanide (HCN), reveal dense areas of active star formation. Still rarer molecules, like H13CN and H13CO+, indicate even denser regions.

By comparing the concentration, distribution, and motion of these molecules, the researchers were able to peel apart the star-forming clouds in Sculptor, revealing that they are much more massive, ten times denser, and far more turbulent than similar clouds in normal spiral galaxies.

These stark differences suggest that it's not just the number of stellar nurseries that sets the throttle for a galaxy to create new stars, but also what kind of stellar nurseries are present. Because the star-forming clouds in Sculptor pack so much material into such a small space, they are simply better at forming stars than the clouds in a galaxy like the Milky Way. Starburst galaxies, therefore, show real physical changes in the star-formation process, not just a one-to-one scaling of star formation with the available reservoir of material.

"These differences have wide-ranging implications for how galaxies grow and evolve," concluded Leroy. "What we would ultimately like to know is whether a starburst like Sculptor produces not just more stars, but different types of stars than a galaxy like the Milky Way. ALMA is bringing us much closer to that goal."

Friday, 13 February 2015

The time-lapse “movie” of Pluto and its largest moon, Charon, below was recently shot at record-setting distances with the Long-Range Reconnaissance Imager (LORRI) on NASA’s New Horizons spacecraft. The movie was made over about a week, from Jan. 25-31, 2015. It was taken as part of the mission’s second optical navigation (“OpNav”) campaign to better refine the locations of Pluto and Charon in preparation for the spacecraft’s close encounter with the small planet and its five moons on July 14, 2015.

Pluto and Charon were observed for an entire rotation of each body; a “day” on Pluto and Charon is 6.4 Earth days. The first of the images was taken when New Horizons was about 3 billion miles from Earth, but just 126 million miles (203 million kilometers) from Pluto—about 30% farther than Earth’s distance from the Sun. The last frame came 6½ days later, with New Horizons more than 5 million miles (8 million kilometers) closer.

The wobble easily visible in Pluto’s motion, as Charon orbits, is due to the gravity of Charon, about one-eighth as massive as Pluto and about the size of Texas.

Faint stars can be seen in background of these images. Each frame had an exposure time of one-tenth of a second, too short to see Pluto’s smaller, much fainter moons. New Horizons is still too far from Pluto and its moons to resolve surface features.

The time-lapse frames in this movie were magnified four times to make it easier to see Pluto and Charon orbit around their barycenter, a mutual point above Pluto’s surface where Pluto and Charon’s gravity cancels out – this is why Pluto appears to “wobble” in space. Charon orbits approximately 11,200 miles (about 18,000 kilometers) above Pluto’s surface.

Each frame had an exposure time of one-tenth of a second, too short to see Pluto’s smaller, much fainter moons.

"These images allow the New Horizons navigators to refine the positions of Pluto and Charon, and they have the additional benefit of allowing the mission scientists to study the variations in brightness of Pluto and Charon as they rotate, providing a preview of what to expect during the close encounter in July," says Alan Stern, the New Horizons principal investigator from the Southwest Research Institute in Boulder, Colorado.

If the icy surface of Pluto's giant moon Charon is cracked, analysis of the fractures could reveal if its interior was warm, perhaps warm enough to have maintained a subterranean ocean of liquid water, according to a 2012 NASA-funded study. Pluto, which was once considered a planet — resides in the Kuiper Belt, a vast collection of frozen objects that orbit our Sun about 30 to 50 astronomical units (AUs) away. One astronomical unit is the distance between the Earth and the Sun, about 150 million kilometers.

Pluto is an extremely distant world, orbiting the sun more than 29 times farther than Earth. With a surface temperature estimated to be about 380 degrees below zero Fahrenheit (around minus 229 degrees Celsius), the environment at Pluto is far too cold to allow liquid water on its surface. Pluto's moons are in the same frigid environment.

"Our model predicts different fracture patterns on the surface of Charon depending on the thickness of its surface ice, the structure of the moon's interior and how easily it deforms, and how its orbit evolved," said Alyssa Rhoden of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "By comparing the actual New Horizons observations of Charon to the various predictions, we can see what fits best and discover if Charon could have had a subsurface ocean in its past, driven by high eccentricity." Rhoden is lead author of a paper on this research now available online in the journal Icarus.

Some moons around the gas giant planets in the outer solar system have cracked surfaces with evidence for ocean interiors – Jupiter's moon Europa and Saturn's moon Enceladus are two examples.

Although temperatures on Pluto's surface hover around -230 °C, but researchers have long wondered whether the dwarf planet might boast enough internal heat to sustain a liquid ocean under its icy exterior.

The team responsible for the Oscar-nominated visual effects at the centre of Christopher Nolan's epic, Interstellar, have turned science fiction into science fact by providing new insights into the powerful effects of black holes. In a paper published today, 13 February, the team describes the innovative computer code that was used to generate the movie's iconic images of the wormhole, black hole and various celestial objects, and explain how the code has led them to new science discoveries.

Using their code, the Interstellar team, comprising London-based visual effects company Double Negative and Caltech theoretical physicist Kip Thorne, found that when a camera is close up to a rapidly spinning black hole, peculiar surfaces in space, known as caustics, create more than a dozen images of individual stars and of the thin, bright plane of the galaxy in which the black hole lives. They found that the images are concentrated along one edge of the black hole's shadow.

These multiple images are caused by the black hole dragging space into a whirling motion and stretching the caustics around itself many times. It is the first time that the effects of caustics have been computed for a camera near a black hole, and the resulting images give some idea of what a person would see if they were orbiting around a hole.

The discoveries were made possible by the team's computer code, which, as the paper describes, mapped the paths of millions of lights beams and their evolving cross-sections as they passed through the black hole's warped spacetime. The computer code was used to create images of the movie's wormhole and the black hole, Gargantua, and its glowing accretion disk, with unparalleled smoothness and clarity.

It showed portions of the accretion disk swinging up over the top and down under Gargantua's shadow, and also in front of the shadow's equator, producing an image of a split shadow that has become iconic for the movie.

This weird distortion of the glowing disk was caused by gravitational lensing--a process by which light beams from different parts of the disk, or from distant stars, are bent and distorted by the black hole, before they arrive at the movie's simulated camera.

This lensing happens because the black hole creates an extremely strong gravitational field, literally bending the fabric of spacetime around itself, like a bowling ball lying on a stretched out bed sheet.

Early in their work on the movie, with the black hole encircled within a rich field of distant stars and nebulae instead of an accretion disk, the team found that the standard approach of using just one light ray for one pixel in a computer code--in this instance, for an IMAX picture, a total of 23 million pixels--resulted in flickering as the stars and nebulae moved across the screen.

Co-author of the study and chief scientist at Double Negative, Oliver James, said: "To get rid of the flickering and produce realistically smooth pictures for the movie, we changed our code in a manner that has never been done before. Instead of tracing the paths of individual light rays using Einstein's equations--one per pixel--we traced the distorted paths and shapes of light beams."

Co-author of the study Kip Thorne said: "This new approach to making images will be of great value to astrophysicists like me. We, too, need smooth images."

Oliver James continued: "Once our code, called DNGR for Double Negative Gravitational Renderer, was mature and creating the images you see in the movie Interstellar, we realised we had a tool that could easily be adapted for scientific research."

In their paper, the team report how they used DNGR to carry out a number of research simulations exploring the influence of caustics--peculiar, creased surfaces in space--on the images of distant star fields as seen by a camera near a fast spinning black hole.

"A light beam emitted from any point on a caustic surface gets focussed by the black hole into a bright cusp of light at a given point," James continued. "All of the caustics, except one, wrap around the sky many times when the camera is close to the black hole. This sky-wrapping is caused by the black hole's spin, dragging space into a whirling motion around itself like the air in a whirling tornado, and stretching the caustics around the black hole many times."

As each caustic passes by a star, it either creates two new images of the star as seen by the camera, or annihilates two old images of the star. As the camera orbits around the black hole, film clips from the DNGR simulations showed that the caustics were constantly creating and annihilating a huge number of stellar images.

The team identified as many as 13 simultaneous images of the same star, and as many as 13 images of the thin, bright plane of the galaxy in which the black hole lives.

These multiple images were only seen when the black hole was spinning rapidly and only near the side of the black hole where the hole's whirling space was moving toward the camera, which they deduced was because the space whirl was 'flinging' the images outward from the hole's shadow edge. On the shadow's opposite side, where space is whirling away from the camera, the team deduced that there were also multiple images of each star, but that the whirl of space compressed them inward, so close to the black hole's shadow that they could not be seen in the simulations.

Thursday, 12 February 2015

An international team of astrophysicists has witnessed a unique event: for the first time, researchers have discovered the formation of a quadruple star system from widely separated fragments of a filamentary gas cloud in the Perseus constellation.

The star system consists of a young star still in an early development phase and three gas clouds which are rapidly condensing by gravitational forces. According the astrophysicists' calculations, each gas cloud will develop into a star in 40,000 years. The stars may be relatively small and only reach around one-tenth the mass of our sun. The space between the individual stars amounts to more than a thousand times the average distance between the sun and the earth.

Unstable quadruple breaks apart

The experts calculated that the two stars which are the shortest distance apart form a stable double system, while the other two stars which are further apart will be catapulted into space after about half a million years. "Star systems with more than three members are unstable and prone to interference," says Jaime Pineda, now at the Max Planck Institute for Extraterrestrial Physics, who is the first author of a study that has just been published inNature. The most probable scenario is that the quadruple will disintegrate and only last for a "short" time.

Not only did the researchers succeed in observing the formation of a multiple star system from a fragmented gas cloud for the first time; it is also unusual how quickly the system is forming. By astronomical standards, the estimated 40,000 years are "exceptionally fast", as Pineda stresses. Nor had anyone been able to observe that stellar systems develop from parts of a filamentary gas cloud until now: "At first, we thought that the fragments wouldn't interact with each other." Often, only a triple system would form.

Unique system studied

Pineda is member of a research collaboration that observed the star system and simulated its genesis and demise. At the time of the discovery, he was working as a postdoctoral researcher in Professor Michael Meyer's group at the ETH Zurich Institute of Astronomy, as was co-author Richard Parker, who determined the stability of the star system on the computer. Astrophysicists from several US and European universities, including Harvard, Yale, Manchester and Liverpool John Moores universities, were also involved in the project. The researchers made their observations at the Very Large Array in the US, which they used to detect emissions originating from ammonia molecules (NH3) in the gas cloud.

"Multiple star systems are very common in our galaxy," says Michael Meyer, professor at the Institute for Astronomy at ETH Zurich. Most researchers, however, have concentrated on the birth and development of individual stars as this is more straightforward. On the other hand, scientists who analyse multiple systems usually tend to focus more on the end result of the star formation. For this reason, this discovery is something very special.

An international team of astrophysicists has witnessed a unique event: for the first time, researchers have discovered the formation of a quadruple star system from widely separated fragments of a filamentary gas cloud in the Perseus constellation.

The star system consists of a young star still in an early development phase and three gas clouds which are rapidly condensing by gravitational forces. According the astrophysicists' calculations, each gas cloud will develop into a star in 40,000 years. The stars may be relatively small and only reach around one-tenth the mass of our sun. The space between the individual stars amounts to more than a thousand times the average distance between the sun and the earth.

Unstable quadruple breaks apart

The experts calculated that the two stars which are the shortest distance apart form a stable double system, while the other two stars which are further apart will be catapulted into space after about half a million years. "Star systems with more than three members are unstable and prone to interference," says Jaime Pineda, now at the Max Planck Institute for Extraterrestrial Physics, who is the first author of a study that has just been published inNature. The most probable scenario is that the quadruple will disintegrate and only last for a "short" time.

Not only did the researchers succeed in observing the formation of a multiple star system from a fragmented gas cloud for the first time; it is also unusual how quickly the system is forming. By astronomical standards, the estimated 40,000 years are "exceptionally fast", as Pineda stresses. Nor had anyone been able to observe that stellar systems develop from parts of a filamentary gas cloud until now: "At first, we thought that the fragments wouldn't interact with each other." Often, only a triple system would form.

Unique system studied

Pineda is member of a research collaboration that observed the star system and simulated its genesis and demise. At the time of the discovery, he was working as a postdoctoral researcher in Professor Michael Meyer's group at the ETH Zurich Institute of Astronomy, as was co-author Richard Parker, who determined the stability of the star system on the computer. Astrophysicists from several US and European universities, including Harvard, Yale, Manchester and Liverpool John Moores universities, were also involved in the project. The researchers made their observations at the Very Large Array in the US, which they used to detect emissions originating from ammonia molecules (NH3) in the gas cloud.

"Multiple star systems are very common in our galaxy," says Michael Meyer, professor at the Institute for Astronomy at ETH Zurich. Most researchers, however, have concentrated on the birth and development of individual stars as this is more straightforward. On the other hand, scientists who analyse multiple systems usually tend to focus more on the end result of the star formation. For this reason, this discovery is something very special.

Wednesday, 11 February 2015

“Dark matter is there,” says says Paolo Zuccon, an assistant professor of physics at MIT. “We just don’t know what it is. AMS has the possibility to shine a light on its features. We see some hint now, and it is within our possibility to say if that hint is true.”

“The new phenomena could be evidence for the long-sought dark matter in the universe, or it could be due to some other equally exciting new science,” says Barry Barish, a professor emeritus of physics and high-energy physics at the California Institute of Technology., who was not involved in the experiments. “In either case, the observation in itself is what is exciting; the scientific explanation will come with further experimentation. If it turns out that the AMS results are due to dark matter, the experiment could establish that dark matter is a new kind of particle."

Researchers at MIT’s Laboratory for Nuclear Science released new measurements this past September that promise to shed light on the origin of dark matter. The MIT group leads an international collaboration of scientists that analyzed two and a half years’ worth of data taken by the Alpha Magnetic Spectrometer (AMS) — a large particle detector mounted on the exterior of the International Space Station — that captures incoming cosmic rays from all over the galaxy. The new AMS results may ultimately help scientists narrow in on the origin and features of dark matter — whose collisions may give rise to positrons.

Among 41 billion cosmic ray events — instances of cosmic particles entering the detector — the researchers identified 10 million electrons and positrons, stable antiparticles of electrons. Positrons can exist in relatively small numbers within the cosmic ray flux. An excess of these particles has been observed by previous experiments — suggesting that they may not originate from cosmic rays, but come instead from a new source. In 2013, the AMS collaboration, for the first time, accurately measured the onset of this excess.

“The new AMS results show unambiguously that a new source of positrons is active in the galaxy,” says Zuccon. “We do not know yet if these positrons are coming from dark matter collisions, or from astrophysical sources such as pulsars. But measurements are underway by AMS that may discriminate between the two hypotheses.”

The new measurements, Zuccon adds, are compatible with a dark matter particle with mass on the order of 1 teraelectronvolt (TeV) — about 1,000 times the mass of a proton.

The team reports the observed positron fraction — the ratio of the number of positrons to the combined number of positrons and electrons — within a wider energy range than previously reported. From the data, the researchers observed that this positron fraction increases quickly at low energies, after which it slows and eventually levels off at much higher energies.

The team reports that this is the first experimental observation of the positron fraction maximum — at 243 to 307 gigaelectronvolts (GeV) — after half a century of cosmic ray experiments.

Zuccon and his colleagues, including AMS’s principal investigator, Samuel Ting, the Thomas D. Cabot Professor of Physics at MIT, detail their results in two papers published today in the journal Physical Review Letters and in a third, forthcoming publication.

Nearly 85 percent of the universe is made of dark matter — matter that somehow does not emit or reflect light, and is therefore invisible to modern telescopes. For decades, astronomers have observed only the effects of dark matter, in the form of mysterious gravitational forces that seem to hold together clusters of galaxy that would otherwise fly apart. Such observations eventually led to the theory of an invisible, stabilizing source of gravitational mass, or dark matter.

The AMS experiment aboard the International Space Station aims to identify the origins of dark matter. The detector takes in a constant flux of cosmic rays, which Zuccon describes as “streams of the universe that bring with them everything they can catch around the galaxy.”

Presumably, this cosmic stream includes leftovers from the violent collisions between dark matter particles. According to theoretical predictions, when two dark matter particles collide, they annihilate, releasing a certain amount of energy that depends on the mass of the original particles. When the particles annihilate, they produce ordinary particles that eventually decay into stable particles, including electrons, protons, antiprotons, and positrons.

As the visible matter in the universe consists of protons and electrons, the researchers reasoned that the contribution of these same particles from dark matter collisions would be negligible. However, positrons and antiprotons are much rarer in the universe; any detection of these particles above the very small expected background would likely come from a new source. The features of this excess — and in particular its onset, maximum position, and offset — will help scientists determine whether positrons arise from astrophysical sources such as pulsars, or from dark matter.

After continuously collecting data since 2011, the AMS team analyzed 41 billion incoming particles and identified 10 million positrons and electrons with energies ranging from 0.5 to 500 GeV — a wider energy range than previously measured.

The researchers studied the positron fraction versus energy, and found an excess of positrons starting at lower energies (8 GeV), suggesting a source for the particles other than the cosmic rays themselves. The positron fraction then slowed and peaked at 275 GeV, indicating that the data may be compatible with a dark matter source of positrons.

Tuesday, 10 February 2015

The team of astronomers, led by Miguel Santander-García (Observatorio Astronómico Nacional, Alcalá de Henares, Spain; Instituto de Ciencia de Materiales de Madrid, Spain, has discovered a close pair of white dwarf stars -- tiny, extremely dense stellar remnants -- that have a total mass of about 1.8 times that of the Sun. This is the most massive such pair yet found and when these two stars merge in the future they will create a runaway thermonuclear explosion leading to a Type Ia supernova.

The Chandrasekhar limit is the greatest mass that a white dwarf star can have and support itself against gravitational collapse. It has a value of about 1.4 times the mass of the Sun. Type Ia supernovae occur when a white dwarf star acquires extra mass -- either by accretion from a stellar companion or by merging with another white dwarf. Once the mass exceeds the Chandrasekhar limit the star loses its ability to support itself and starts to contract. This increases the temperature and a runaway nuclear reaction occurs and blows the star to pieces.

The team who found this massive pair actually set out to try to solve a different problem. They wanted to find out how some stars produce such strangely shaped and asymmetric nebulae late in their lives. One of the objects they studied was the unusual planetary nebula known as Henize 2-428 shown above.

"When we looked at this object's central star with ESO's Very Large Telescope, we found not just one but a pair of stars at the heart of this strangely lopsided glowing cloud," says coauthor Henri Boffin from ESO.

This supports the theory that double central stars may explain the odd shapes of some of these nebulae, but an even more interesting result was to come.

"Further observations made with telescopes in the Canary Islands allowed us to determine the orbit of the two stars and deduce both the masses of the two stars and their separation. This was when the biggest surprise was revealed," reports Romano Corradi, another of the study's authors and researcher at the Instituto de Astrofísica de Canarias (Tenerife, IAC - http://www.iac.es/).

They found that each of the stars has a mass slightly less than that of the Sun and that they orbit each other every four hours. They are sufficiently close to one another that, according to the Einstein's theory of general relativity, they will grow closer and closer, spiralling in due to the emission of gravitational waves, before eventually merging into a single star within the next 700 million years.

The resulting star will be so massive that nothing can then prevent it from collapsing in on itself and subsequently exploding as a supernova. "Until now, the formation of supernovae Type Ia by the merging of two white dwarfs was purely theoretical," explains David Jones, coauthor of the article and ESO Fellow at the time the data were obtained. "Thepair of stars in Henize 2-428 is the real thing!"

"It's an extremely enigmatic system," concludes Santander-García. "It will have important repercussions for the study of supernovae Type Ia, which are widely used to measure astronomical distances and were key to the discovery that the expansion of the Universe is accelerating due to dark energy".

"We know that dark matter is needed in our Galaxy to keep the stars and gas rotating at their observed speeds," says Dr. Miguel Pato, at Technische Universität München. "However, we still do not know what dark matter is composed of. This is one of the most important science questions of our times."

The ubiquitous presence of dark matter in the universe is today a central tenet in modern cosmology and astrophysics. Its existence in galaxies was robustly established in the 1970s with a variety of techniques, including the measurement of the rotation speed of gas and stars, which provides a way to effectively 'weigh' the host galaxy and determine its total mass. These measurements showed that the visible matter only accounts for a fraction of the total weight, the predominant part is delivered by dark matter.

Applying this technique to our own Galaxy is possible, and the existence of dark matter in the outer parts of the Milky Way is well ascertained. But up to now it has proven very difficult to establish the presence of dark matter in the innermost regions.

The diameter of our Galaxy is about 100,000 lightyears. Our Solar System is located at a distance of about 26,000 light years from the center. Coming closer to the center of our galaxy it becomes increasingly difficult to measure the rotation of gas and stars with the needed precision.

Now scientists from the Technische Universität München (TUM), Stockholm University, Universidad Autónoma de Madrid, ICTP South American Institute for Fundamental Research, São Paulo and University of Amsterdam have obtained for the first time a direct observational proof of the presence of dark matter in the innermost part the Milky Way, including at the Earth's location and in our own 'cosmic neighborhood'.

In a first step they created the most complete compilation of published measurements of the motion of gas and stars in the Milky Way. Then they compared the measured rotation speed with that expected under the assumption that only luminous matter exists in the Galaxy. The comparison clearly showed that the observed rotation cannot be explained unless large amounts of dark matter exist around us, and between us and the galactic center.

Possessing a very strong statistical evidence, even at small galactocentric distances, the results open a new avenue for the determination of dark matter distribution inside the Galaxy. With future astronomical observations, the method will allow to measure the distribution of dark matter in our Galaxy with unprecedented precision.

"This will permit to refine the understanding of the structure and evolution of our Galaxy. And it will trigger more robust predictions for the many experiments worldwide that search for dark matter particles," says Miguel Pato, who meanwhile moved to The Oskar Klein Centre for Cosmoparticle Physics at the Stockholm University.

The image at the top of the page displays the rotation curve tracers over a photograph of the disc of the Milky Way as seen from the Southern Hemisphere. The tracers are colour-coded in blue or red according to their relative motion with respect to the Sun. The spherically symmetric blue halo illustrates the dark matter distribution inferred from the analysis.